<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>

<div id="app">
  <h1>{{counter}}</h1>
  <button @click="increment">+</button>
  <button @click="decrement">-</button>
</div>

<script src="../js/vue%20.js"></script>
<script>
  const app = new Vue({
    el:'#app',
    data:{
      counter: 0
    },
    methods: {
      increment() {
        this.counter++
      },
      decrement() {
        this.counter--
      }
    }
  })
</script>
</body>
</html>